1. Field of the Invention.
The present invention relates generally to a coupling assembly for fuel lines and the like, and more particularly to a coupling assembly for interconnecting adjacent conduits in which the coupling assembly is coated with a hard metallic ductile conductive coating for preventing the buildup of an electrostatic charge between the conduits, and wherein the flange to which the coupling is mounted is selectively coated with a hard anodized coating or other non-electrically conductive coating to improve the lighting-strike characteristics of the coupling by preventing arcing between the flanges and between each flange and the coupling.
2. Description of the Related Art.
When conveying fluid, such as jet fuel, between interconnected fuel lines, it is necessary to provide electrical conductivity between the fuel lines to prevent the buildup of an electrostatic charge between the fuel lines. If an electrostatic charge were to build up, an electric spark could occur, thereby causing the fuel to ignite. The build up of static electricity poses a problem in other applications which use conduits for material transfer. For example, in sandblasters, if the hose used to discharge the sand is not grounded, static electricity may build up sufficiently in the hose so that an electric shock and/or arcing may occur at the coupling between hose lengths, causing personal injury or property damage. This situation is discussed in more detail in U.S. Pat. No. 4,658,326.
In order to overcome the problem of static buildup in fuel lines, U.S. Pat. No. 4,487,462, the contents of which are incorporated herein by reference, discloses a coupling that provides electrical contact between adjacent fuel lines. A pair of bonding jumpers is provided each of which includes i) an annular ring having a plurality of bonding jumper contact flanges that engage a surface of the threaded coupling, and ii) a plurality of spaced retaining tangs which snap into a retaining groove in the coupler and the nut. The nut also includes a plurality of circumferentially spaced contact tangs which are interspersed with the retaining tangs and which contact the outer end of the coupling beyond the threads.
Another requirement for aircraft fuel lines, which is not necessarily a requirement for couplings used in other applications, is that the coupling be self-retained after installation in such a manner that the coupling will not loosen despite vibrations or other forces to which the coupling may be subjected. U.S. Pat. No. 3,669,472, the contents of which are incorporated herein by reference, discloses one of many patented devices that have been developed to prevent relative rotation of coupling members. This device relates to a coupling having an annular ring with spring fingers which releasably engage notches on the edge of a male connector to minimize the chance of the coupling becoming unthreaded due to vibrations or other forces on the coupling. A separate releasable bonding ring is provided between the two coupling elements.
A related aspect of the coupling of fuel lines to reduce the buildup of static electricity is the contact between the coupling members and the fuel lines. This point of contact is preferably redundant so as to reduce the likelihood that the contact will fail, and must be capable of being rotated with the coupling members as they are threaded together. One method for providing such contact was developed by the Assignee of the present invention and sold as the 15J02 and 15J Series couplings. The 15J02 and 15J Series couplings are constructed of male and female threaded coupling members and a detent ring with a single resilient detent mounted to one of the coupling members. The other coupling member includes a surface facing the detent ring with spaced notches for engaging with the detent as the coupling members are rotated relative to each other. In order to provide electrical contact between the coupling members and the fuel lines, a split ring with a multi-sided bonding wire mounted therein is mounted in each end of one coupling member. The bonding wires provide multiple electrical contact points between the fuel lines and coupling members.
As shown in FIG. 1, U.S. Pat. Nos. 4,808,117 and 4,928,202, the contents of which are incorporated herein by reference, relate to a threaded coupling that is essentially a combination of the teachings of the aforementioned U.S. Pat. Nos. 3,669,472 and 4,487,462, and the 15J02 Series couplings. A pair of assembly sealing flanges 14 and 16 are connected to the ends of fuel lines (not shown). The flanges each have a cylindrical skirt 18 and 20 which is sealingly attached to the fuel lines by any suitable means. Each flange is provided with a peripheral recess 22 and 24 for receiving O-rings 26 and 28. Recess 22 is formed between a pair of peripheral ribs 30 and 32 and recess 24 is formed between a pair of similar ribs 34 and 36. The confronting ends of the fuel lines are interconnected by means of a threaded coupler 38 and nut 40 which cooperate to draw the coupler and nut axially toward each other to secure them together and to form a fluid-tight seal. Within coupler 38 is a circumferential retaining groove 48 receiving a split ring 50.
The nut or female member 40 has an inwardly projecting peripheral flange 52 on its end and internal threads 54 which receive threads 44 of coupler 38. The peripheral flange 52 serves as a stop for split ring 56, which is mounted in female coupling member 40. Split rings 50 and 56 have internal grooves 58 and 88 within which bonding rings 60 and 76 are received respectively. Bonding rings 60 and 76 have a generally non-circular configuration and have upturned spaced ears 62, 64, 80 and 82 which are squeezed together to insert the bonding rings into grooves 58 and 88, and which project upwardly through apertures 66, 68, 84 and 86. Split rings 50 and 56 serve to retain the coupling members 38 and 40 on sealing flanges 14 and 16. The flat sides 70 and 78 of bonding rings 60 and 76 engage the cylindrical skirts 18 and 20 of sealing flange 14 and 16 to provide multiple electrical contact points between the coupling members 38 and 40 and the sealing flanges. Flange 48 has a plurality of spaced notches 72 which are utilized with a bonding jumper 74.
Nut 40 is provided with a recess 90 within which bonding jumper 74 is received. The bonding jumper has a plurality of equally spaced spring detents 92, each of which has a curved end 94. The bonding jumper is also provided with spaced notches 96 into which the edge 91 is bent to form a crimp to prevent relative rotation of bonding jumper 74 with respect to nut 40. As nut 40 is tightened, the curved ends of spring detents 92 come into engagement with flange 46 of coupler 38 and engage notches 72. As the nut is drawn tight, the force of each spring detent against flange 46 and notches 72 increases. This arrangement provides a redundant electrical contact between nut 40 and coupling 38. Bonding jumper 74 also serves to minimize the possibility that the nut will turn in a reverse direction accidentally due to vibrations or other forces.
In commercial versions of couplings of the type disclosed in U.S. Pat. Nos. 4,808,117 and 4,928,202, the threads of the coupling members are coated with a non-electrically-conducting dry-lube coating in order to enable the members to be threadably engaged without binding. Thus, the redundant electrical contact provided by bonding jumper 74 is necessary because no electrical contact is provided between the coupling members through the threads.
Accordingly, it would be desirable to have a coupling for preventing electrostatic build up between adjacent conduits in which the electrical contact is provided through the threads so that a bonding jumper is not required for preventing such electrostatic buildup. It would also be desirable to have such a coupling in which there is a low coefficient of friction between the threaded surfaces so as to avoid binding of the threads during threading.
An alternative type of coupling for fuel lines is commonly known as a clamshell coupling. This type of coupling is described in detail in, for example, U.S. Pat. Nos. 4,249,786 and 4,346,428, the contents of each of which are incorporated herein by reference. A clamshell coupling includes two semi-circular segments which are hinged together at one pair of adjacent ends. The other pair of adjacent ends is provided with an interlocking latch so as to latch the two semicircular segments together in a continuous annular closure member. In order to prevent a buildup of static electricity between the adjacent conduits, a pair of bonding wires establishes an electrical connection between the clamshell coupling and each of the conduits.
While this configuration is generally effective at preventing a buildup of static electricity between the conduits, due to the dangerous situation presented by any such buildup, it would be beneficial to have an improved system for preventing the buildup of static electricity between conduits in a clamshell coupling.
Lighting strike characteristics are very important for fuel lines couplings, especially aircraft fuel line couplings. In the event that an aircraft is struck by lighting or experiences a static discharge, the coupling must not arc internally or externally, which might result in ignition of fuel vapors in the fuel line or in the outside environment, i.e., inside a partially filled fuel cell, and possibly a catastrophic failure of the aircraft. Because it is impractical to test fuel lines under actual lighting strike conditions, laboratory tests are performed in which the coupling is struck by simulated lighting. Accordingly, it would be desirable to have a fuel line coupling capable of withstanding such a simulated lighting strike with minimal or no internal or external arcing in order to reduce the possibility of a catastrophic failure due to an actual lighting strike while the coupling is in use.